Recirculating paint spray system



March 6, 1962 w. E. MITCHELL 3,023,968

RECIRCULATING PAINT SPRAY SYSTEM Filed Sept. 22, 1958 2 Sheets-Sheet 1,

II I INVENTOR- TOP/V6) W. E. MITCHELL RECIRCULATING PAINT SPRAY SYSTEMMarch 6, 1962 2 She'ets-$heet 2 Filed Sept. 22, 1958 United StatesPatent C) M 3,023,968 RECIRJULATING PAINT SPRAY SYSTEM Walter E.Mitchell, Detroit, Mich, assignor to General Motors Corporation,Detroit, Mich, a corporation of Deiaware Filed Sept. 22, 1953, er. No.762,410 6 Claims. (Cl. 239125) This invention relates to fluiddistribution systems and more particularly to a system of therecirculating type for supplying coating materials such as paints,enamels, lacquers and the like to a plurality of spray guns located at aplurality of spaced spray painting stations.

in conventional practice a paint circulating system for use in spraypaintir g consists essentially of a paint mixing and storage tank, amain pipe line extending from the tank along a series of paintingstations or spray booths and returning to the tank, pump means forcirculating paint in the pipe line under pressure, a spray gun at eachspray station connected to the main pipe line by means of supply ductssuch as a hose, and a pressure regulating device connected in the supplyducts for insuring that paint is supplied to each spray gun at asatisfactory spray gun operating pressure.

A paint circulating system of the type described above is inadequate foruse in spraying paints having a tendency to settle rapidly such as theacrylic type paints and where the various spray guns may be usedintermittently, because the paint pigment and other solids in the paintwithin the supply ducts leading from the main paint supply line to thespray guns tend to settle out when a particular spray gun is not in usefor a substantial period of time with a result that when the spray gunis again put into use the paint is off-color. a

It is, therefore, the basic object of this invention to provide a paintcirculating system for use in spray painting at a series of paintspraying stations wherein the paint at all points of the system iscaused to move at a predetermined minimum rate sufficient to preventsettling of the pigments and other solids of the paint regardless of thenumber of spray guns in operation, and wherein the paint is supplied toeach spray gun at a constant predetermined pressure.

This and other objects of this invention are accomplished by providing acirculating system including a mixing and supply tank, a main supplyline leading from the supply tank, extending along a series of paintspraying stations or booths and returning to the supply tank, and pumpmeans for circulating paint in the main supply line at a predeterminedrelatively high pressure. A separate secondary return line is providedwhich extends along the main supply line and leads to the supply andmixing tank. A cross circuit or line is provided having an inlet portionconnected to the main supply line and an outlet portion connected to thesecondary return line at each of a series of paint spray stationssituated along these lines whereby paint may flow therethrough from themain supply line to the secondary return line. A spray gun is connectedin each of the cross circuits to the inlet and outlet portions thereofby means of a Y-type connection whereby paint may flow into the sprayguns when the latter are in operation while maintaining continuous paintfiow through the cross circuits from the main supply line to thesecondary return line. A pressure regulator is connected in each of thecross circuit inlet portions to insure that the paint is fed into eachspray gun at a predetermined pressure below the main line pressure. Eachcross circuit is further provided with a restricted portion in theoutlet portion thereof to control paint flow and avoid by-passing of allof the main supply line capacity through the first few branch lines.

$323,958 Patented Mar. 6, 1962 ICC An important feature of the systemresides in the aforementioned separate secondary return line which isprogressively graduated or varied in diameter in accordance with thenumber of cross circuits feeding paint to it to insure that the paint isat all time flowing at all points of the return line toward the supplytank at a predetermined minimum rate in lineal feet at which rate thesolids of the paint will not tend to settle. Thus, the return line isprovided with a relatively small diameter at the point where but asingle cross circuit feeds paint to it such that the paint will flowtherethrough at at least the predetermined minimum rate, and withprogressively increased diameters at points downstream as the number ofcross circuits feeding paint to the return line increase to maintain theminimum flow rate in the entire line. By maintaining the pressure in themain supply line at a predetermined flow and by properly adjusting thepipe diameters of the secondary return line and the size of theaforementioned restriction in the cross circuits, the paint is caused toflow in all lines of the circulating system at at least thepredetermined lineal rate whether or not the various spray guns are inuse and while spraying paint to the various spray guns at apredetermined pressure.

Other objects and advantages of this invention will be apparent from thefollowing description of a preferred embodiment, reference being made tothe accompanying drawings in which:

FIGURE 1 is a perspective view of the circulating system.

FIGURE 2 is an enlarged view of a branch line involved in the system.

FIGURE 3 is an exploded view of a spray gun and portions of a branchline including a restricted portion.

FIGURE 4 is an exploded view of a connection of a branch line includinga restricted portion.

Referring to FIGURE 1 the paint circulating system of the presentinvention includes a pair of mixing and supply tanks 10 and 12. Withineach tank is a mixing or agitating member (not shown) of suitableconfiguration attached to a shaft 14 and driven by an electric motor 16.Conduits 18 and 26 are provided for venting the tanks. The tanks 1i and12. are each connected to a pump 22 through a two-way valve 24 wherebyeither tank may be used to feed paint to the pump. The pump may be ofany suitable design, and preferably an air pump such as the BinksManufacturing Company type 31V air pump which is capable of moving thepaints without adversely affecting their quality. A compressed airsupply means 26 is provided for operating the pump.

Leading from the pump is a main relatively high pressure supply line 28which includes a surge tank 30, a check valve 32 and encircles a seriesof spray painting stations or booths indicated generally at 33, 34, 35,36,

38, 40, 42 and 44 and then leads back to the mixing tanks 10 and 12through a two-way valve 46 whereby the return flow of paint may bedirected to either tank. A

back pressure valve 48 is provided in the return portion of the mainsupply line 28, the purpose of which will be hereinafter fullydescribed.

A separate secondary paint return line 50 is provided which is branchedto form legs 52 and 54 each extending along portions of the main supplyline 28 which passes along the spray booth area and which leads to eachof the supply tanks 10 and 12 through a two-way valve 56 whereby theflow of paint in the secondary return line 59 may be directed to eitherof the mixing tanks.

Connected across the main supply line 28 and the sec ondary return line50 at each of the spray painting stations as, for example, the stationgenerally indicated at 33, is a cross circuit 58 having connectedtherein a spray gun 60.

As is shown in greater detail in FIGURE 2 the cross circuit 58 includesan inlet portion including a rigid section 62 having connected therein ashut-off valve 64 and a pressure regulating or reducing valve 66. Thevalve 66 isof the known adjustable automatic pressure reducing type,which when set for a given pressure on the outlet side of the valvefunctions to open or close with decrease or increase of pressure fromthe predetermined point on such outlet side of the valve to bring thepressure back to a given point. The inlet portion also includes aflexible hose section 68 connected to the rigid section 62 and to a Yconnection 70 connected to the spray gun 68. A compressed air supplyhose 61 is connected to the spray gun for atomizing the paint in thepaint spraying operation, in a manner well known in the art. The crosscircuit also includes an outlet portion including a flexible hose 72 anda rigid section 74 connected to the secondary return line 50. Shut-offvalves 76 and 78 are provided to permit the hose sections 68 and 72 tobe disconnected without allowing paint to run out of the rigid sections62 and 74.

An important aspect of the system is the provision of a restrictingmeans in the outlet portion of the cross circuit. This restriction mayconveniently be in the form of an orifice as connected between the Yconnection 73 and the outlet hose portion 72 as shown in FIGURE 3. Thisrestricting means may also be an orifice 82 connected between thecut-off valve 76 and the hose 72 as is shown in FIGURE 4.

in operation of the system thus far described, the paint is admitted tothe tanks and 12 and thoroughly mixed. The pump 22 is placed intooperation and the valve 24 is set to enable one of the tanks to supplypaint to the pump. The dual tank arrangement described permits one ofthe tanks to supply paint to the pump while the other tank is used tomix fresh paint. The pump 22 then pumps the paint into the main supplyline 28 which in a specific installation is 1 /2" in diameter, at about80 pounds per square inch gauge. This paint feed pressure may varybetween 60 to 88 pounds pressure depending upon the distance between themixing tanks and the spray booths. The paint then encircles the spraybooth area within the line 28 at a lineal rate of not less thanapproximatey one lineal foot per second and returns to either tank 10and 12 as determined by the setting of the valve 46.

The paint also flows through each of the cross circuits 58 to thesecondary return line 50 from whence it returns to one of the tanks 10and 12 depending on the setting of the valve 56.

Within each of the cross circuits 58 the pressure of the paint isreduced to about 15 pounds per square inch by the pressure regulator 66which may be of any suitable design well known in the art. The paint,now at about 15 pounds per square inch, passes through the hose 68 tothe spray gun 60. If the spray gun is in operation, a portion, of thepaint stream flows into the spray gun and the balance thereof flows intothe secondary return line 59 through the orifices 80 or 82. Of course,if the spray gun is not in use, all of the paint stream entering thecross circuit fiows into the secondary return line 58. The purpose ofthese orifices is to provide a back pressure in the branch line at apoint after the spray guns to avoid bypassing all of the maincirculating line capacity through the first few branch lines. Since onlya portion of the paint flowing through a cross circuit is utilized inthe spraying operation when the spray gun is in use, the pressures inthe cross circuits are not appreciably affected by intermittent use ofthe spray guns.

The branch line portions 52 and 54 of the secondary return line arevaried in diameter in accordance with the volume of the paint flowingthereto from the various cross circuits So that the paint may flow inthe secondary line 50 at a substantially lineal uniform rate at whichsolids in the paint will not settle. Thus, the portion 43 of the branchline 52 of the secondary return line 50 between the cross. circuits ofthe spray stations 44 and 42, the spray station most remote from thepump 22, may be of a minimum diameter of /4". The pipe section 41 of thebranch line 50 between the cross circuits at the paint stations 42 andmay be the pipe section 39 between the branch line at the paint stations40 and 38 may be /2", and the pipe section 37 between the cross circuitsat the paint station 38 and the jointure of the branch lines '2 and 54-may be /8". The line 54 is similarly graduated.

By adjusting the size of the restricting orifice 80, and suitablygraduating the secondary return line 50, the paint flow is balanced sothat substantially equal lineal flow rates are maintained in the supplyline 28 and a secondary return line with the result that the paint is atall times flowing at all points of the system at at least the minimumpredetermined minimum rate at which the settling of the solids in thepaint will not occur, and a-satisfactory volume of paint at apredetermined pressure is provided at all the spray guns whether or notthey are in use.

In the event that the main supply line 28 is relatively long and has arelatively large number of cross circuits 58 connected therein andtherefore the pressure drop in this line is too high to provide for theproper functioning of the last cross circuit connected thereto, therestricting valve 48 is utilized to provide a sufficient back pressurein the line 28 after the cross circuits to provide for a sufiicientlyhigh pressure throughout the main supply line to permit a properfunctioning of all of the spray guns.

In some instances where the paint tends to clog the orifices 80 and 82the orifice may be replaced by a relatively long flexible tube ofrestricted diameter whereby a suitable back pressure is effected using alarger restricted area. Thus, it has been found that a 0.06 orifice 80may be replaced by a A3" tube of suitable length.

In the event that an exceptionally long secondary return line 56 isnecessarily involving a large number of cross circuits 58 connectedthereto, a booster pump 84 (FIG- URE i) may be used to avoid anexcessive pressure build up in the line. The operating pressure in thesecondary return line 50 may also be increased by providing a restrictedsection 86 between the spray gun and the Y fitting 70. The use of theorifice at this point results in an increase in the regulated pressurethrough the cross circuit lines while maintaining the same fluid flowthrough the spray guns with the result that the pressure in the returnline 50 is correspondingly increased.

In the event that it is desired to use the circulating system for a hotspray painting operation, heaters 88 (FIG- URE l) of suitable design areinstalled in the main supply line at suitable intervals and the mainsupply line is suitably insulated which is effective in maintaining theentire system at a suitably hot temperature.

The various dimensions, pressure, flow rates, e-tc., mentioned hereinare for the purpose of illustration and it is readily apparent that theprecise dimensions to be used will depend upon the needs of a particularpaint spray operation. The various components referred to such aspressure regulator valves and the like are intended to refer to deviceswhose function and design are well known in the art.

While this invention has been described in terms of certain preferredembodiments it will be understood that the scope of the invention is notintended to be limited thereby except as defined in the followingclaims.

I claim:

1. A fluid distributing and circulating system comprising a main supplyline, a separate return line, a plurality of material applying devices,a plurality of cross circuits each including inlet and outlet portionsrespectively connected to said supply line and return line and bothconnected to a said device, pressure reducing means connected in each ofsaid inlet portions and operative to control the volume of materialpassing from the supply line to said devices, and a fiuicl control meansconnected in each of said outlet portions and including a constantlyopen passage of restricted size such that the pressure in said outletportion is always less than the pressure at the devices and the pressureat each of said devices is substantially equal, said return line havingan increased internal cross-sectional area with an increase in thenumber of cross circuits feeding paint thereto.

2. A pressure balanced paint distributing and circulating systemcomprising a main supply line, a plurality of paint applying devices, aseparate return line, a plurality of cross circuits each including inletand outlet portions respectively connected to said supply line andreturn line and both connected to a said device, pressure reducing meansconnected in each of said inlet portions and operative to control thevolume of paint passing from said supply line to said devices, and fluidcontrol means connected in each of said outlet portions and including aconstantly open passage of restricted size such that the pressure insaid outlet portion is always less than the pressure at the devices andthe pressure at each of said devices is substantially equal, said returnline being graduated to have a greater internal cross-sectional areawith an increase in the number of cross circuits feeding paint thereto,the pressure in said main supply line, said fluid control means and thegraduation of said return line being adjusted so that the paint throughthe system flows at least at a predetermined minimum rate.

3. Claim 2 wherein said main supply line includes a restricting meansdownstream of the last cross circuit connected thereto whereby thepressure in said main supply line at this point is at least equal to thepressure maintained by said pressure reducing means in said crosscircuits.

4. Claim 2 wherein said main supply line is insulated and includes heattransfer means for heating the paint in said main supply line.

5. A pressure balanced paint distributing and circulating systemcomprising a paint mixing and supply tank; a main supply line leadingfrom said tank, encircling a plurality of spray painting stations andreturning to said tank; pump means connected in said main supply linecirculating paint from said tank through said main supply line, aseparate secondary return line extending along said main supply line inthe vicinity of said spray stations and leading to said tank; aplurality of paint applying devices; a plurality of cross circuits eachincluding inlet and outlet portions respectively connected to saidsupply line and secondary return line and both said portions connectedto a said device, pressure reducing means connected in each of saidinlet portions operative to control the volume of paint passing from thesupply line to each of said devices, and fluid control means connectedin each of said outlet portions and including a constantly open passageof restricted size such that the pressure in said outlet portion isalways less than at the devices and the pressure at each of said devicesis substantially equal; said return line being of progressively greaterinternal cross-sectional area with each increase in the number of crosscircuits feeding paint thereto; the pressure in said main supply line,said fluid control means and the diameter of said secondary return linebeing adjusted so that the paint throughout the system flows at at leasta predetermined rate at which the solids of the paint circulating in thesystem will not settle.

6. A fluid distributing and circulating system comprising a main supplyline, a separate return line, a plurality of material applying devices,a plurality of cross circuits each including inlet and outlet portions,respectively connected to said supply line and said return line and bothconnected to said device, pressure reducing means connected in each ofsaid inlet portions operative to control the volume of material passingfrom said supply line to said devices, and fluid control means connectedin each of said inlet portions operative to cause the pressure in saidoutlet portions to be less than the pressure at said devices, saidreturn line being graduatedto have a greater internal cross-sectionalarea with an increase in the number of cross circuits feeding materialthereto.

References Cited in the file of this patent UNITED STATES PATENTS2,244,686 Garrison et al. June 10, 1941 2,263,913 Bargeboer Nov. 25,1941 2,378,184 Carlson June 12, 1945 2,488,089 Mayo Nov. 15, 19492,513,081 Clark et al June 27, 1950 2,537,681 Lawrence Jan. 9, 19512,740,469 Colestock Apr. 3, 1956 2,747,555 Brunner May 29, 1956

